meristems of Ferns as a P hylogenetic Study. 355 
having rectangular bases ; (3) that they undergo T division, 
and therefore (4) the whole segmentation of the wing is of a 
more complicated type than in the typical leptosporangiate 
Ferns : the whole wing is more massive, and the centre of 
construction more deeply seated. 
These being the results of examination of Todea barbara , a 
peculiar interest attaches to the examination of similar points 
in the ‘filmy’ species of Todea ( = Leptopteris , Presl.), and to 
the question whether the filmy character is to be taken as any 
indication of an affinity to the Hymenophyllaceae. I have 
already described the conformation of the base of the leaf of 
Todea superba 1 , and in this respect, as also in the structure of 
its apex, it is essentially similar to the more robust T. bar- 
bara ; but the pinnae and pinnules with their wings are more 
delicate : stomata and intercellular spaces are absent from the 
wings, which consist of but few layers of cells, and accordingly 
they have that delicate pellucid character which is described 
as ‘ filmy. 5 
The wings on the lower part of the phyllopodium are not 
largely developed, and appear when mature to be about three 
layers of cells in thickness : similarly, the wings of the mature 
pinnae and pinnules are three layers in thickness near to the 
midrib, but tail off towards the margin to a single layer : thus 
it is only at the margin that the wings actually attain the 
character of the simpler Hymenophyllaceae. As regards their 
development, no marginal series is to be seen on any part of the 
leaf when young ; it is only subsequently that a rather ir- 
regular marginal series appears, and in their first segmentations 
the marginal cells follow the polypodiaceous type (Figs. 61, 
62) ; but in some cases (Figs. 63, 64) the segmentation is 
rather that of wings of a more bulky character : later, however, 
as the wings grow more extended, they become thinner at the 
margin, and transverse segmentation such as is seen in the 
Hymenophyllaceae becomes the rule (Figs. 65, 66, 67) ; thus, 
as regards their development, these filmy wings of Todea 
superba show first, though imperfectly, the characters of the 
1 Phil. Trans. 1884, Part II, p. 578. 
B b 
